In a Fourier transform infrared spectrophotometer (hereinafter simply referred to as the “FTIR”), which is one type of spectrophotometer, an interfering light whose amplitude temporally changes is produced by a Michelson interferometer including a fixed mirror and a moving mirror. This light is thrown onto a sample, and a transmitted light or reflected light is detected as an interferogram. The interferogram is subjected to Fourier transformation to obtain an absorption spectrum with the horizontal axis representing the wave number and the vertical axis representing the intensity of light (e.g. absorbance or transmittance).
In the FTIR, which uses infrared light, absorption peaks due to unwanted components (e.g. water vapor or carbon dioxide) existing in the measurement optical path overlap the absorption peaks due to proper sample. Given this problem, an absorption spectrum with no sample is first obtained using the same measurement optical system as used in an actual measurement of the sample, and then this absorption spectrum (i.e. the background spectrum) is subtracted from an absorption spectrum obtained by an actual measurement with the sample set in the system, to obtain an absorption spectrum that reflects the true absorption by the sample (Patent Documents 1 and 2). Accordingly, in the transmission measurement using the FTIR, it is necessary to successively perform the three steps of performing a background measurement with no sample (this measurement is often called a “blank measurement” since no sample is set in the system), setting a sample in a sample chamber, and performing an actual measurement of the sample. The background measurement may be performed after the actual measurement of the sample, in which case the process of removing the sample from the sample chamber is required.
The recently used FTIRs are normally composed of an FTIR main unit for performing a measurement on a sample to collect data and a personal computer in which device-controlling and data-processing software programs for controlling the main unit and processing the collected data are installed. (This computer is hereinafter referred to as a “control PC.”) To perform a background measurement or a sample measurement using this type of FTIR, an operator needs to perform an operation for performing the measurement by using a keyboard or a pointing device of the control PC. On the other hand, when setting a sample, the operator needs to set it at a proper position within the sample chamber of the FTIR main unit, using a holder, cell or similar device depending on the kind of the sample (e.g. solid, liquid, powder or thin film). If the FTIR main unit is placed remotely from the control PC for the convenience of system installation, the aforementioned three-stage process requires the operator to move from the control PC to the FTIR main unit and then back to the control PC. This is a troublesome and inefficient task.
FTIRs can obtain an absorption spectrum over a predetermined wavelength range through one cycle of the reciprocal movement of the moving mirror. However, the S/N ratio achieved by a single-cycle measurement is rather low. Therefore, in general, the reciprocal movement of the moving mirror is repeated many times to accumulate multiple sets of data of collected interferograms, and then subject the accumulated data to Fourier transformation to create an absorption spectrum with a high S/N ratio. Due to such a process, the measurement requires a considerable length of time. In order to perform the aforementioned three processes without wasting time between processes, it is desirable for an operator to stand by the FTIR main unit and wait for the completion of, for example, the background measurement. However, this significantly lowers the work efficiency since, as just explained, this measurement requires a considerable length of time.    Patent Document 1: JP-A 2002-22536    Patent Document 2: JP-A 2008-275326